BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The embodiments relate to a method for driving an image pickup apparatus, and, more
specifically, to a method for driving an image pickup apparatus capable of performing
focus detection in an image pickup area.
Description of the Related Art
[0002] A remarkable development is currently seen in the field of image pickup apparatuses.
An image pickup apparatus is known in which focus detection adopting a pupil division
method is performed using an image sensor obtained by forming a micro-lens in each
pixel of the image pickup apparatus (Japanese Patent Laid-Open No.
2001-124984).
[0003] According to Japanese Patent Laid-Open No.
2001-124984, the image sensor is provided at an expected imaging area of an imaging lens. In
addition, each pixel in the image sensor includes a photoelectric conversion element
A and a photoelectric conversion element B, and each photoelectric conversion element
is arranged in such a way as to be substantially conjugate to a pupil of the imaging
lens with the micro-lenses of the image sensor formed on an imaging lens side.
[0004] Here, the photoelectric conversion element A receives a light beam that has passed
through a portion of the pupil of the imaging lens. On the other hand, the photoelectric
conversion element B receives a light beam that has passed through a portion of the
pupil different from the portion through which the light beam received by the photoelectric
conversion element A has passed. During the focus detection, signals are independently
read from the photoelectric conversion elements A and B of a plurality of pixels,
and two images are generated by the light beams that have passed through the different
positions of the pupil of the imaging lens. In addition, image information can be
obtained by adding the signals of the two photoelectric conversion elements A and
B.
[0005] Since the signals of the photoelectric conversion elements A and the signals of the
photoelectric conversion elements B are sequentially read independently in Japanese
Patent Laid-Open No.
2001-124984, the time at which the signals of the photoelectric conversion elements A are received
and the time at which the signals of the photoelectric conversion elements B are received
is different from each other.
[0006] More specifically, when a signal in a certain row is to be read, first, reset signals
of the photoelectric conversion elements A are output. Next, light signals of the
photoelectric conversion elements A are output. Similarly, reset signals of the photoelectric
conversion elements B are output, and then light signals of the photoelectric conversion
elements B are output. By this operation, a time difference of tens to hundreds of
microseconds is generated between the signals of the photoelectric conversion elements
A and the signals of the photoelectric conversion elements B. Therefore, an error
is generated between the signals of the photoelectric conversion elements A and the
signals of the photoelectric conversion elements B, which makes it difficult to increase
the accuracy of the focus detection.
SUMMARY OF THE INVENTION
[0007] The present invention in its first aspect provides a method for driving an image
pickup apparatus as specified in claims 1 to 10.
[0008] The present invention in its second aspect provides a method for driving an image
pickup apparatus as specified in claim 11.
[0009] The present invention in its third aspect provides an image pickup apparatus as specified
in claim 12.
[0010] The present invention in its fourth aspect provides an image pickup apparatus as
specified in claim 13.
[0011] Further features of the present invention will become apparent from the following
description of exemplary embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Fig. 1 is a block diagram illustrating the entirety of an image pickup apparatus
according to a first embodiment.
[0013] Fig. 2 is a timing chart of the image pickup apparatus according to the first embodiment.
[0014] Fig. 3 is a block diagram illustrating the entirety of an image pickup apparatus
according to a second embodiment.
[0015] Fig. 4 is a timing chart of the image pickup apparatus according to the second embodiment.
[0016] Fig. 5 is a block diagram illustrating pixels in an image pickup apparatus according
to a third embodiment.
[0017] Fig. 6 is a timing chart of the image pickup apparatus according to the third embodiment.
[0018] Fig. 7 is a block diagram illustrating pixels in an image pickup apparatus according
to a fourth embodiment.
[0019] Fig. 8 is a timing chart of the image pickup apparatus according to the fourth embodiment.
DESCRIPTION OF THE EMBODIMENTS
[0020] Embodiments will be described with reference to the drawings. In the following description,
an example in which each pixel is configured using an n-channel metal-oxide-semiconductor
(MOS) transistor will be described. The embodiments may be applied to a case in which
each pixel is configured using a p-channel MOS transistor. In this case, voltage and
the like are changed as necessary.
First Embodiment
[0021] Fig. 1 is an equivalent circuit diagram of an image pickup apparatus according to
the present embodiment. A photoelectric conversion unit 100 includes a plurality of
photoelectric conversion elements, namely a first photoelectric conversion element
101A and a second photoelectric conversion element 101B here. As each photoelectric
conversion element, a photodiode may be used.
[0022] Transfer transistors 102A and 102B are provided for the plurality of photoelectric
conversion elements, respectively, and transfer signals of the corresponding photoelectric
conversion elements to an input node 103 of an amplification unit 104. A lens array
(not illustrated) including a plurality of lenses is provided for each of a plurality
of photoelectric conversion units above the photoelectric conversion elements. The
lenses of each lens array focus light onto the plurality of photoelectric conversion
elements in the same photoelectric conversion unit. The plurality of photoelectric
conversion elements included in each photoelectric conversion unit are provided at
different positions when viewed in plan.
[0023] The amplification unit 104 amplifies the signals transferred to the input node 103
and outputs the signals to a common output line 107. A MOS transistor may be used
for the amplification unit 104.
[0024] A reset transistor 105 supplies reset voltage to the input node 103 of the amplification
unit 104. A selection transistor 106 controls electrical continuity between the amplification
unit 104 and the common output line 107.
[0025] A current source 108 is electrically connected to the common output line 107. The
current source 108 supplies bias current to the amplification unit 104, and a source
follower can be configured by the amplification unit 104 and the current source 108.
[0026] Drive lines 109A and 109B, a drive line 110, and a drive line 111 are connected to
the gates of the transfer transistors 102A and 102B, the reset transistor 105, and
the selection transistor 106, respectively. Driving pulses are supplied, sequentially
row by row or randomly, to each gate from a vertical scanning circuit 112.
[0027] A column circuit receives signals from the common output line 107. The column circuit
is connected to the common output line 107 directly, through a switch, or through
a buffer. The signals processed by the column circuit are sequentially output to an
output amplifier 115 by a horizontal scanning circuit 114 and then output to the outside.
[0028] A main operation of the column circuit is to execute inverting amplification on the
signals from the common output line 107 using gain determined by a capacitance value
of an input capacitor 116 and a capacitance value of a feedback capacitor 117. Furthermore,
it is possible to perform a virtual grounding operation. In addition, it is possible
to perform a correlated double sampling (CDS) operation through a clamping operation
using the input capacitor 116.
[0029] Next, an example of the column circuit will be described. A first node of the input
capacitor 116 is electrically connected to the common output line 107, and a second
node of the input capacitor 116 is electrically connected to an inverting input node
of an operational amplifier 119. A first node of the feedback capacitor 117 is electrically
connected to the inverting input and the second node of the input capacitor 116. A
second node of the feedback capacitor 117 is electrically connected to an output node
of the operational amplifier 119.
[0030] A switch 118 is provided along a feedback path between the inverting input node and
the output node of the operational amplifier 119 in order to control an electrical
connection between the two. The feedback capacitor 117 and the switch 118 are provided
parallel to each other.
[0031] A power supply 120 supplies reference voltage Vref to a non-inverting input node
of the operational amplifier 119. Storage capacitors 121 to 124 are capacitors that
store outputs of the operational amplifier 119. Switches 125 to 128 are provided along
electrical paths between the storage capacitors 121 to 124 and the operational amplifier
119, respectively, and control electrical continuity between the output node of the
operational amplifier 119 and the storage capacitors 121 to 124, respectively. Switches
129 to 132 receive signals from the horizontal scanning circuit 114 and output the
signals stored in the storage capacitors 121 to 124, respectively, to horizontal output
lines 139 and 140.
[0032] The output amplifier 115 is provided as necessary. The output amplifier 115 obtains
a difference between the signals output from the column circuit to the horizontal
output lines 139 and 140 and outputs the difference to the outside.
[0033] A driving pulse PC0R is supplied to the switch 118. A driving pulse PTN is supplied
to the switches 126 and 128. A driving pulse PTSA is supplied to the switch 125. A
driving pulse PTSAB is supplied to the switch 127.
[0034] Next, driving of the image pickup apparatus illustrated in Fig. 1 will be described
with reference to Fig. 2. The driving pulses cause the corresponding elements to be
conductive at high level.
[0035] First, at a time T = t1, driving pulses PTXA and PTXB supplied to the drive lines
109A and 109B, respectively, are switched to the high level. At this time, because
a driving pulse PRES supplied to the drive line 110 is at the high level, the photoelectric
conversion elements 101A and 101B are reset.
[0036] Next, at a time T = t2, the driving pulses PTXA and PTXB are switched to low level.
Charge storage periods of the photoelectric conversion elements 101A and 101B begin
at this timing. Since the driving pulse PRES remains at the high level, a reset operation
for the input node 103 of the amplification unit 104 continues.
[0037] After storage is performed for a certain period of time, signals are supplied to
the common output line 107 row by row or in a plurality of rows at a time.
[0038] At a time T = t3, a driving pulse PSEL supplied to the drive line 111 of the selection
transistor 106 is switched to the high level, and the selection transistor 106 becomes
conductive. Therefore, a signal according to the potential of the input node 103 of
the amplification unit 104 is output to the common output line 107.
[0039] By switching the driving pulse PRES supplied to the drive line 110 of the reset transistor
105 to the low level at a time T = t4, the reset operation for the input node 103
of the amplification unit 104 is cancelled. A reset signal level is then supplied
to the common output line 107 and input to the column circuit. At this time, the operational
amplifier 119 is in a virtual grounding state. More specifically, the driving pulse
PC0R is at the high level, and the switch 118 is closed. The operational amplifier
119 is in a state in which the output reference voltage Vref is buffered, and the
reset signal level is supplied to the input capacitor 116 in this state.
[0040] Next, the driving pulse PC0R is switched to the low level at a time T = t5, and the
driving pulse PTN is switched from the low level to the high level at a time T = t6
in order to close the switches 126 and 128. The driving pulse PTN is switched from
the high level to the low level at a time T = t7 in order to open the switches 126
and 128. By this operation, the output reference voltage Vref is substantially supplied
to the storage capacitors 122 and 124, and then the storage capacitors 122 and 124
and the output node of the operational amplifier 119 become non-conductive.
[0041] At a time T = t8, the driving pulse PTXA is switched to the high level and optical
charge of the first photoelectric conversion element 101A is transferred to the input
node 103 of the amplification unit 104, and, at a time T = t9, the driving pulse PTXA
is switched to the low level. By this operation, the optical charge of the first photoelectric
conversion element 101A is transferred to the input node 103. Therefore, a signal
based on the optical charge is supplied to the column circuit by the amplification
unit 104 and the common output line 107. By this operation, a signal for focus detection
can be generated in the common output line 107.
[0042] The column circuit outputs a value obtained by multiplying a change in voltage by
inverse gain at a ratio of a capacitance value C0 of the input capacitor 116 to a
capacitance value Cf of the feedback capacitor 117. More specifically, when a change
in the voltage of the common output line 107 is denoted by ΔVa (negative) and the
output of the operational amplifier 119 is denoted by V(A), the following expression
(1) is obtained:

[0043] Next, at a time T = t10, the driving pulse PTSA is switched from the low level to
the high level to close the switch 125. At a time T = t11, the driving pulse PTSA
is switched from the high level to the low level to open the switch 125. By this operation,
the storage capacitor 121 stores a signal.
[0044] At a time T = t12, the driving pulse PTXA is switched to the high level, and the
driving pulse PTXB is switched to the high level at least for a part of a period in
which the driving pulse PTXA is at the high level. By this operation, optical charges
of both the photoelectric conversion elements 101A and 101B can be simultaneously
transferred to the input node 103. By this operation, a signal for forming an image
can be generated in the common output line 107. The input node 103 of the amplification
unit 104 is not reset until the optical charges of both the photoelectric conversion
elements 101A and 101B are simultaneously transferred to the input node 103 after
the signal of the photoelectric conversion element 101A is transferred.
[0045] The charges transferred to the input node 103 of the amplification unit 104 are supplied
to the column circuit, just as when only the charge of the photoelectric conversion
element 101A is transferred. When a change in the potential of the common output line
107 is denoted by ΔVa + b (negative) and the output potential of the operational amplifier
119 is denoted by V(A + B), the following expression (2) is obtained:

[0046] At a time T = t14, the driving pulse PTSAB is switched from the low level to the
high level to close the storage capacitor 122. Next, at a time T = t15, the driving
pulse PTSAB is switched from the high level to the low level to open the storage capacitor
122. By this operation, the potential V(A + B) of the output node of the operational
amplifier 119 can be written to the storage capacitor 123.
[0047] Therefore, a difference voltage between capacitances CTSAB and CTN can be obtained
by the following expression (3):

This corresponds to a result obtained by adding the signals of two photoelectric
conversion elements included in a photoelectric conversion unit. A signal corresponding
to one pixel when an image is captured using a plurality of photoelectric conversion
elements included in a photoelectric conversion unit is obtained.
[0048] In addition, by obtaining a potential difference between the storage capacitors 121
and 122, which is obtained by the following expression (4), a signal of only the photoelectric
conversion element 101A can be obtained:

The signal obtained by the photoelectric conversion element 101A corresponds to information
regarding a focused light beam that has passed through a part of a pupil of an imaging
lens. Furthermore, by obtaining a potential difference between the two, which is obtained
by the following expression (5), a signal of only the photoelectric conversion element
101B can be obtained:

The signal obtained by the photoelectric conversion element 101B corresponds to information
regarding a focused light beam that has passed through a part of the pupil of the
imaging lens. The plurality of photoelectric conversion elements included in each
photoelectric conversion unit are provided at different positions when viewed in plan.
Focus detection can be performed on the basis of the pieces of information of the
photoelectric conversion elements 101A and 101B regarding the two light beams.
[0049] The above calculation may be performed inside the image pickup apparatus or may be
performed by a signal processing unit after the relevant signals are output from the
image pickup apparatus. However, the signal of only the photoelectric conversion element
101A and the result obtained by adding the signals of the photoelectric conversion
elements 101A and 101B are obtained in the image pickup apparatus.
[0050] Next, at a time T = t16, the driving pulse PRES is switched to the high level to
cause the reset transistor 105 to be conductive and reset the potential of the input
node 103.
[0051] The signals stored in the storage capacitors 121 to 124 are read by sequentially
causing driving pulses 133 and 134 synchronized with a pulse PH to be conductive after
a time T = t17. According to the present embodiment, since the output amplifier 115
that can execute a difference process is provided in a later stage of the horizontal
output lines 139 and 140, a difference between the signals stored in the storage capacitors
121 and 122 can be output to the outside of the image pickup apparatus. Furthermore,
a difference between the signals stored in the storage capacitors 123 and 124 can
be output to the outside of the image pickup apparatus. Therefore, noise generated
in the horizontal output lines 139 and 140 can be reduced. However, the output amplifier
115 need not necessarily have a configuration in which a differential output is obtained,
and may be simply a buffer stage. Furthermore, the output amplifier 115 need not be
provided. Thereafter, signals in the rows are sequentially scanned by the horizontal
scanning circuit 114 and supplied to the horizontal output lines 139 and 140.
[0052] It is to be noted that an example in which, as the order of reading, the added signals
of the photoelectric conversion elements 101A and 101B are read after the signal of
only the photoelectric conversion element 101A is read has been described, the order
may be switched. By reading the signal of only the photoelectric conversion element
101A first, better signals can be obtained. This is because the signals are more susceptible
to leakage current due to the capacitors and the switches when a period for which
the signals are stored in the storage capacitors 121 to 124 is longer.
[0053] The characteristics of the present embodiment lie in the operations in a period from
the time t11 to the time t15.
[0054] In Japanese Patent Laid-Open No.
2001-124984, the following operation is disclosed. A signal of a first photoelectric conversion
element is written to a storage capacitor, a horizontal transfer operation is performed,
and the signal is read out to the outside of an image pickup apparatus. Next, a reset
transistor executes a reset operation. Thereafter, a signal of a second photoelectric
conversion element is written to the storage capacitor, the horizontal transfer operation
is performed, and the signal is read out to the outside of a sensor. The reset transistor
then executes the reset operation again.
[0055] In this case, a reading time difference (tens to hundreds of microseconds) corresponding
to one row is undesirably generated between the reading of the signal of the first
photoelectric conversion element and the reading of the signal of the second photoelectric
conversion element.
[0056] In the present embodiment, when the signal of the photoelectric conversion element
101A has been read, the signal is written to a storage capacitor at the time T = t11.
At the time T = t12, while the signal of the photoelectric conversion element 101A
remains held at the input node 103, the signals of both the photoelectric conversion
elements 101A and 101B are read at the time T = t12. In doing so, the reading time
can be significantly (several microseconds) decreased. Furthermore, the time difference
in the signal reading between the photoelectric conversion elements 101A and 101B
can decrease, thereby increasing the accuracy of the focus detection.
[0057] In addition, the secondary characteristics of the present embodiment lie in the operations
in a period from the time T = t8 to the time T = t15. By simultaneously switching
the driving pulses PTXA and PTXB to the high level, the following effects can be produced.
However, the driving pulse PTXA need not be necessarily switched to the high level
in a second operation.
[0058] First, as a first effect, the potential of the input node 103 increases because of
capacitive coupling between a drive line of a transfer transistor and the input node
103 when the gate potential of the transfer transistor switches from the low level
to the high level. In the present embodiment, the gate potential of the two transfer
transistors 102A and 102B switches from the low level to the high level. Therefore,
an increase in the potential of the input node 103 is larger than when only one transfer
transistor is used. When the potential of the input node 103 has become high, it becomes
easier for the charges of the photoelectric conversion elements 101A and 101B to be
transferred to the input node 103. Therefore, the transfer efficiency can be improved.
[0059] In particular, when one pixel for capturing an image has been divided into two photoelectric
conversion elements as in the configuration of the image pickup apparatus according
to the present embodiment, a potential barrier for signal charge is often provided
between the photoelectric conversion elements 101A and 101B. Due to this potential
barrier, the potential distribution of the photoelectric conversion elements 101A
and 101B becomes complex. Therefore, residual charge after transfer tends to be generated,
and accordingly fixed pattern noise or random noise can be generated. On the other
hand, by switching the driving pulses PTXA and PTXB to the high level at the same
time, an effect can be produced in which the fixed pattern noise or the random noise
is reduced while the potential of the input node is high.
[0060] As a second effect, a difference in storage time between the photoelectric conversion
elements 101A and 101B can be decreased. For example, in the configuration disclosed
in Japanese Patent Laid-Open No.
2001-124984, the storage times of the two photoelectric conversion elements undesirably become
different from each other. On the other hand, as in the present embodiment, by making
the timings at which all transfer gates corresponding to photoelectric conversion
elements used to add signals are turned off be substantially the same when the input
node 103 adds the signals, the storage times can be the same. This is especially effective
in a configuration in which a signal for the focus detection is obtained in an image
pickup area of the image pickup apparatus.
[0061] Although a signal of a single photoelectric conversion element is used to generate
a signal for the focus detection in the present embodiment, signals of a plurality
of photoelectric conversion elements may be used when a larger number of photoelectric
conversion elements are included in one photoelectric conversion unit. However, signals
of all the photoelectric conversion elements included in one photoelectric conversion
unit cannot be used to obtain a signal for the focus detection. This holds true for
the following embodiments.
[0062] In addition, although signals of all the photoelectric conversion elements (two here)
included in one photoelectric conversion unit are read in the second operation, the
method for reading signals is not limited to this. It is sufficient if a signal of
a photoelectric conversion element that has not read in a first operation is read.
This, too, holds true for the following embodiments.
Second Embodiment
[0063] Fig. 3 is an equivalent circuit diagram of an image pickup apparatus according to
a second embodiment.
[0064] A difference from the first embodiment is the configurations of the photoelectric
conversion unit and the column circuit. The number of photoelectric conversion elements
included in one photoelectric conversion unit is 3, and accordingly the number of
storage capacitors included in the column circuit is 6. Components having the same
functions as in the first embodiment are given the same reference numerals, and detailed
description thereof is omitted.
[0065] A photoelectric conversion unit 200 includes photoelectric conversion elements 101A
to 101C. Since the number of photoelectric conversion elements included in one pixel
for capturing an image is larger than that in the first embodiment, more accurate
focus detection is possible.
[0066] Transfer transistors 102A to 102C that transfer charges of the photoelectric conversion
elements 101A to 101C are included. As a driving pulse for the transfer transistor
102C, a driving pulse PTXC is added.
[0067] A column circuit 210 includes a storage capacitor 201 for storing signals of the
photoelectric conversion element 101A to 101C added to one another. In addition, a
storage capacitor 202 for storing a noise level is included. Switches 203 to 206 corresponding
to these components are also included.
[0068] Next, a method for driving the image pickup apparatus according to the present embodiment
will be described with reference to Fig. 4. Because a basic operation is the same
as that described with reference to Fig. 2, differences from the first embodiment
will be mainly described.
[0069] At the time T = t12, both the driving pulses PTXA and PTXB are switched to the high
level. By this operation, the signals of the photoelectric conversion elements 101A
and 101B are added at the input node 103. Although both the driving pulses PTXA and
PTXB are switched to the high level here, only the driving pulse PTXB may be switched
to the high level. Next, at the time T = t16, all of the driving pulses PTXA, PTXB,
and PTXC are switched to the high level. By this operation, the charges of the photoelectric
conversion elements 101A to 101C are added at the input node 103. At the time T =
t17, all of the driving pulses PTXA, PTXB, and PTXC are switched to the low level.
By this operation, the storage periods of the photoelectric conversion elements 101A
to 101C can be the same, namely as a period from the time t2 to the time t17.
[0070] After the added signals of the photoelectric conversion elements 101A to 101C are
read, a signal of only the photoelectric conversion element 101A or added signals
of the photoelectric conversion elements 101A and 101B may be read.
[0071] By reading the signal of only the photoelectric conversion element 101A, the added
signals of the photoelectric conversion elements 101A and 101B, and the added signals
of the photoelectric conversion elements 101A to 101C in this order, better signals
can be obtained. This is because the signals are more susceptible to leakage current
due to the capacitors and the switches when a period for which the signals are stored
in the storage capacitors 121 to 124, 201, and 202 is longer.
Third Embodiment
[0072] Fig. 5 is an equivalent circuit diagram of an image pickup apparatus according to
a third embodiment. A difference from the first and second embodiments is that the
amplification unit 104 is shared by a plurality of photoelectric conversion elements
included in different photoelectric conversion units.
[0073] In Fig. 5, a first photoelectric conversion unit including photoelectric conversion
elements 501A and 501B and a second photoelectric conversion unit including photoelectric
conversion elements 502A and 502B are included. Light collected by a first micro-lens
is incident on the plurality of photoelectric conversion elements 501A and 501B included
in the first photoelectric conversion unit and light collected by a second micro-lens
is incident on the plurality of photoelectric conversion elements 502A and 502B included
in the second photoelectric conversion unit.
[0074] Transfer transistors 503A, 503B, 504A, and 504B are provided for the photoelectric
conversion elements 501A, 501B, 502A and 502B, respectively. As lines for supplying
driving pulses to the transfer transistors 503A, 503B, 504A, and 504B, drive lines
505A, 505B, 506A, and 506B, respectively, are provided.
[0075] According to this configuration, the amplification unit 104, the reset transistor
105, and the selection transistor 106 can be shared by a plurality of pixels for capturing
an image. In doing so, the number of transistors included in one pixel for capturing
an image can be decreased. As a result, the area of the photoelectric conversion elements
can be increased.
[0076] With respect to an operation for sequentially reading the photoelectric conversion
elements 501A, 501B, 502A, and 502B, signals can be read as signals in different rows
by performing an operation that is basically the same as the reading described with
reference to Fig. 2. More specifically, after a signal of the photoelectric conversion
element 501A is read in the first photoelectric conversion unit, signals of the photoelectric
conversion elements 501A and 501B are added to each other at the input node 103. In
doing so, both a signal for the focus detection and signals for capturing an image
can be generated. Next, after a signal of the photoelectric conversion element 502A
is read in the second photoelectric conversion unit, signals of the photoelectric
conversion elements 502A and 502B are added to each other at the input node 103. In
doing so, both a signal for the focus detection and signals for capturing an image
can be generated.
[0077] Furthermore, in the present embodiment, the amplification unit 104 is shared by the
two photoelectric conversion units that are different from each other. Therefore,
the signals of the photoelectric conversion elements 501A and 502A are added at the
input node 103 and signals of the photoelectric conversion elements 501B and 502B
may be added to each other at the input node 103. A specific example of a driving
timing is illustrated in Fig. 6. Characteristics of the present embodiment will be
mainly described. Here, a driving pulse PTXA (505A) is supplied to the transfer transistor
503A, and a driving pulse PTXB (505B) is supplied to the transfer transistor 503B.
Furthermore, a driving pulse PTXA (506A) is supplied to the transfer transistor 504A,
and a driving pulse PTXB (506B) is supplied to the transfer transistor 504B.
[0078] At the time T = t8, the driving pulses PTXA (505A) and PTXA (506A) are switched from
the low level to the high level. Thereafter, at the time T = t9, the driving pulses
PTXA (505A) and PTXA (506A) are switched from the high level to the low level. By
this operation, the signals of the photoelectric conversion element 501A and 502A
included in different photoelectric conversion units are added to each other at the
input node 103. These signals can be used as the signals for the focus detection.
[0079] Next, at the time T = t12, the driving pulses PTXA (505A), PTXB (505B), PTXA (506A),
and PTXB (506B) are switched from the low level to the high level. Thereafter, at
the time T = t13, the driving pulses PTXA (505A), PTXB (505B), PTXA (506A), and PTXB
(506B) are switched from the low level to the high level. By this operation, the signals
of all the photoelectric conversion elements 501A, 501B, 502A, and 502B included in
different photoelectric conversion units are added to each other at the input node
103. These signals are used as the signals for capturing an image.
[0080] Since the signals for the focus detection are obtained by adding signals of a plurality
of photoelectric conversion elements included in different photoelectric conversion
units with one another through this operation, the S/N ratio improves. Therefore,
more accurate focus detection is possible.
[0081] It is to be noted that although an example in which signals of two pixels for capturing
an image are added to each other has been described in the present embodiment, the
same effect can be produced even when the number of pixels is 3 or more.
Fourth Embodiment
[0082] Fig. 7 is an equivalent circuit diagram of an image pickup apparatus according to
a fourth embodiment. A difference of the present embodiment from the third embodiment
is that a switch for electrically connecting a plurality of input nodes 103 to one
another is provided. Components having functions similar to those of the configurations
according to the first to third embodiments are given similar reference numerals,
and detailed description thereof is omitted.
[0083] In Fig. 7, a first photoelectric conversion unit includes photoelectric conversion
elements 701A and 701B. A second photoelectric conversion unit includes photoelectric
conversion elements 702A and 702B. A third photoelectric conversion unit includes
photoelectric conversion elements 721A and 721B. A fourth photoelectric conversion
unit includes photoelectric conversion elements 722A and 722B. An amplification unit
707 shared by the first and second photoelectric conversion units is provided. An
amplification unit 727 shared by the third and fourth photoelectric conversion units
is provided.
[0084] Transfer transistors 703A, 703B, 704A, 704B, 723A, 723B, 724A, and 724B are provided
for these photoelectric conversion elements, respectively. Drive lines 705A, 705B,
706A, 706B, 725A, 725B, 726A, and 726B for driving these transfer transistors, respectively,
are provided.
[0085] A switch 740 electrically connects input nodes of the amplification units 707 and
727 to each other. The switch 740 is controlled by a drive line 741.
[0086] Fig. 8 is a driving pulse diagram of Fig. 7. Here, only elements corresponding to
the first photoelectric conversion unit and the third photoelectric conversion unit
will be extracted and described. The second and fourth photoelectric conversion units
can perform the same driving. A driving pulse PTXA (705A) is a pulse supplied to the
drive line 705A. A driving pulse PTXB (705B) is a pulse supplied to the drive line
705B. A driving pulse PTXA (725A) is a pulse supplied to the drive line 725A. A driving
pulse PTXB (725B) is a pulse supplied to the drive line 725B. A driving pulse PVADD
(741) is a pulse supplied to the drive line 741.
[0087] In Fig. 8, an example in which signals of the photoelectric conversion elements 701A
and 721A included in the first photoelectric conversion unit and the third photoelectric
conversion unit, respectively, are added to each other is illustrated.
[0088] The driving pulse PVADD (741) is kept at the high level during a period illustrated
in Fig. 8. That is, the inputs nodes of the amplification units 707 and 727 are electrically
connected to each other constantly.
[0089] At the time T = t8, the driving pulses PTXA (705A) and PTXA (725A) are switched from
the low level to the high level. Thereafter, at the time T = t9, the driving pulses
PTXA (705A) and PTXA (725A) are switched from the high level to the low level. By
this operation, the signals of the photoelectric conversion elements 701A and 721A
included in different photoelectric conversion units are transferred to the corresponding
amplification units 707 and 727, respectively. Since the switch 740 is closed, the
signals are added to each other. These signals can be used as the signals for the
focus detection.
[0090] Next, at the time T = t12, the driving pulses PTXA (705A), PTXB (705B), PTXA (725A),
and PTXB (725B) are switched from the low level to the high level. Thereafter, at
the time T = t13, the driving pulses PTXA (705A), PTXB (705B), PTXA (725A), and PTXB
(725B) are switched from the high level to the low level. By this operation, signals
of the plurality of photoelectric conversion elements 701A, 701B, 721A, and 721B included
in different photoelectric conversion units are transferred to the corresponding amplification
units 707 and 727. Since the switch 740 is closed, all the signals are added to one
another. These signals can be used as the signals for capturing an image.
[0091] In the present embodiment, the switch for electrically connecting the plurality of
input nodes is added. This is desirable when signals of the same color are separated
from one another in an image pickup apparatus including color filters, that is, for
example, when the image pickup apparatus includes color filters arranged in a Bayer
pattern. This is because it is possible to add the signals of photoelectric conversion
elements of the same color that are arranged separately from one another to one another.
Therefore, not only the focus detection but also the S/N ratio of image signals can
be improved, thereby realizing accurate focus detection while obtaining high-quality
image information.
[0092] It is to be noted that although an example in which two input nodes are connected
to each other has been described in the present embodiment, the same effect can be
produced even when the number of input nodes connected to one another is 3 or more.
[0093] Although the specific embodiments have been described, the present invention is not
limited to the above embodiments and may be modified or altered in various ways. For
example, the circuit configurations of pixels are not limited to those described above,
and a configuration in which selection and deselection are switched by switching the
potential of an input node using a reset unit without including a selection unit may
be adopted. Furthermore, although a configuration in which an operational amplifier
is included as a column circuit has been described, a simple configuration such as
that of a common-source amplification circuit may be adopted, instead. Alternatively,
various modifications are possible such as a configuration in which a plurality of
gain stages are provided and a configuration in which an adding between a gain stage
and a buffer stage is used. In addition, although one common output line is provided
for a pixel column in the above embodiments, a plurality of common output lines may
be provided for one pixel column.
[0094] While the present invention has been described with reference to exemplary embodiments,
it is to be understood that the invention is not limited to the disclosed exemplary
embodiments. The scope of the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures and functions.
A signal for focus detection is generated by a first operation, in which a signal
of at least one photoelectric conversion element (101A) included in a photoelectric
conversion unit (100) is read to an input node (103) of an amplification unit (104)
and the signal is supplied to a common output line (107) by the amplification unit
and signals for forming an image are generated by a second operation, in which a signal
of another photoelectric conversion element (101B) included in the same photoelectric
conversion unit as that including the at least one photoelectric conversion element
from which the signal has been read in the first operation is read to the input node
of the amplification unit while holding the signal read in the first operation using
the amplification unit and the signals are supplied to the common output line by the
amplification unit.
1. A method for driving an image pickup apparatus that includes a plurality of photoelectric
conversion units (100), each including a plurality of photoelectric conversion elements
(101A, 101B), a plurality of amplification units (104), each of which is shared by
the plurality of photoelectric conversion elements included in each of the plurality
of photoelectric conversion units and amplifies signals of the plurality of photoelectric
conversion elements, and a plurality of common output lines (107) that output signals
obtained from the plurality of amplification units, the method comprising:
generating a signal for focus detection by a first operation, in which a signal of
at least one of the plurality of photoelectric conversion elements included in each
of the plurality of photoelectric conversion units is read to an input node (103)
of a corresponding one of the plurality of amplification units and the signal is then
supplied to a corresponding one of the plurality of common output lines by the amplification
unit; and
generating a signal for forming an image by a second operation, in which at least
a signal of a photoelectric conversion element from which the signal has not been
read in the first operation and that is included in the same photoelectric conversion
unit as that including the at least one photoelectric conversion element from which
the signal has been read in the first operation is read to the input node of the amplification
unit and added to the signal read in the first operation while holding the signal
read in the first operation using the amplification unit and the added signals are
supplied to the common output line by the amplification unit.
2. The method for driving an image pickup apparatus according to Claim 1,
wherein a potential of the input node of the amplification unit is not reset in a
period between the first operation and the second operation.
3. The method for driving an image pickup apparatus according to Claim 1 or 2,
wherein the image pickup apparatus includes a lens array including a plurality of
lenses provided for each of the plurality of photoelectric conversion units, and the
lenses of each lens array focus light onto the plurality of photoelectric conversion
elements included in the same photoelectric conversion unit.
4. The method for driving an image pickup apparatus according to any of Claims 1 to 3,
wherein one of the plurality of amplification units is shared by a plurality of photoelectric
conversion elements included in different photoelectric conversion units.
5. The method for driving an image pickup apparatus according to Claim 4,
wherein, in the first operation, a signal of at least one photoelectric conversion
element included in a first photoelectric conversion unit and a signal of at least
one photoelectric conversion element included in a second photoelectric conversion
unit are added to each other by one of the plurality of amplification units shared
by the first and second photoelectric conversion units, and
wherein, in the second operation, signals of a plurality of photoelectric conversion
elements included in the first photoelectric conversion unit and signals of a plurality
of photoelectric conversion elements included in the second photoelectric conversion
unit are added to one another by the one of the plurality of amplification units shared
by the first and second photoelectric conversion units.
6. The method for driving an image pickup apparatus according to any of Claims 1 to 5,
wherein the image pickup apparatus includes a switch (740) that electrically connects
input nodes of the plurality of amplification units to one another.
7. The method for driving an image pickup apparatus according to Claim 6,
wherein, by closing the switch in the first operation, the input nodes of the plurality
of amplification units are electrically connected to one another and signals of the
input nodes connected to one another are added to one another, and
wherein, by closing the switch in the second operation, the input nodes of the plurality
of amplification units are electrically connected to one another and signals of the
input nodes connected to one another are added to one another.
8. The method for driving an image pickup apparatus according to any of Claims 1 to 7,
wherein the image pickup apparatus includes a plurality of transfer gates (102A, 102B),
each of which transfers a signal of each of the plurality of photoelectric conversion
elements to an input node of a corresponding one of the plurality of amplification
units, and
wherein, in the second operation, one of the plurality of transfer gates corresponding
to a photoelectric conversion element from which a signal is transferred in the second
operation is conductive for at least a part of a period in which one of the plurality
of transfer gates corresponding to a photoelectric conversion element from which a
signal is transferred in the first operation is conductive.
9. The method for driving an image pickup apparatus according to any of Claims 1 to 8,
wherein the plurality of photoelectric conversion elements included in each of the
plurality of photoelectric conversion units are provided at different positions when
viewed in plan.
10. The method for driving an image pickup apparatus according to any of Claims 1 to 9,
wherein potential of the input node of the amplification unit is reset before the
first operation, and a difference process is performed on the signals obtained by
the first operation and the second operation using a reset signal output to the common
output line by the amplification unit after the resetting.
11. A method for driving an image pickup apparatus that includes a plurality of photoelectric
conversion units (100), each including a plurality of photoelectric conversion elements
(101A, 101B), a plurality of amplification units (104), each of which is shared by
the plurality of photoelectric conversion elements included in each of the plurality
of photoelectric conversion units and amplifies signals of the plurality of photoelectric
conversion elements, and a plurality of common output lines (107) that output signals
obtained from the plurality of amplification units, the method comprising:
generating a signal for focus detection by a first operation, in which a signal of
at least one of the plurality of photoelectric conversion elements included in each
of the plurality of photoelectric conversion units is read to an input node (103)
of a corresponding one of the plurality of amplification units and the signal is then
supplied to a corresponding one of the plurality of common output lines by the amplification
unit; and
generating a signal for forming an image by a second operation, in which at least
a signal of a photoelectric conversion element from which the signal has not been
read in the first operation and that is included in the same photoelectric conversion
unit as that including the at least one photoelectric conversion element from which
the signal has been read in the first operation is read to the input node of the amplification
unit and added to the signal read in the first operation while holding the signal
read in the first operation using the amplification unit and the added signals are
supplied to the common output line by the amplification unit,
wherein, in the second operation, one of the plurality of transfer gates (102A, 102B)
corresponding to a photoelectric conversion element from which a signal is transferred
in the second operation is conductive for at least a part of a period in which one
of the plurality of transfer gates corresponding to a photoelectric conversion element
from which a signal is transferred in the first operation is conductive, and
wherein potential of the input node of the amplification unit is reset before the
first operation, and a difference process is performed on the signals obtained by
the first operation and the second operation using a reset signal output to the common
output line by the amplification unit after the resetting.
12. An image pickup apparatus comprising:
a plurality of photoelectric conversion means (100), each including a plurality of
photoelectric conversion elements (101A, 101B);
a plurality of amplification means (104), each of which is shared by the plurality
of photoelectric conversion elements included in each of the plurality of photoelectric
conversion means and amplifies signals of the plurality of photoelectric conversion
elements; and
a plurality of common output lines (107) arranged to output signals obtained from
the plurality of amplification means,
wherein a signal for focus detection is generated by a first operation, in which a
signal of at least one of the plurality of photoelectric conversion elements included
in each of the plurality of photoelectric conversion means is read to an input node
(103) of a corresponding one of the plurality of amplification means and the signal
is then supplied to a corresponding one of the plurality of common output lines by
the amplification means, and
wherein signals for forming an image are generated by a second operation, in which
at least a signal of a photoelectric conversion element from which the signal has
not been read in the first operation and that is included in the same photoelectric
conversion means as that including the at least one photoelectric conversion element
from which the signal has been read in the first operation is read to the input node
of the amplification means and added to the signal read in the first operation while
holding the signal read in the first operation using the amplification means and the
added signals are supplied to the common output line by the amplification means.
13. An image pickup apparatus comprising:
a plurality of photoelectric conversion means (100), each including a plurality of
photoelectric conversion elements (101A, 101B);
a plurality of amplification means (104), each of which is shared by the plurality
of photoelectric conversion elements included in each of the plurality of photoelectric
conversion means and amplifies signals of the plurality of photoelectric conversion
elements; and
a plurality of common output lines (107) arranged to output signals obtained from
the plurality of amplification means,
wherein a signal for focus detection is generated by a first operation, in which a
signal of at least one of the plurality of photoelectric conversion elements included
in each of the plurality of photoelectric conversion means is read to an input node
(103) of a corresponding one of the plurality of amplification means and the signal
is then supplied to a corresponding one of the plurality of common output lines by
the amplification means,
wherein signals for forming an image are generated by a second operation, in which
at least a signal of a photoelectric conversion element from which the signal has
not been read in the first operation and that is included in the same photoelectric
conversion means as that including the at least one photoelectric conversion element
from which the signal has been read in the first operation is read to the input node
of the amplification means and added to the signal read in the first operation while
holding the signal read in the first operation using the amplification means and the
added signals are supplied to the common output line by the amplification means,
wherein a lens array including a plurality of lenses provided for each of the plurality
of photoelectric conversion means is included, and the lenses of each lens array focus
light onto the plurality of photoelectric conversion elements that are included in
the same photoelectric conversion means and that are provided at different positions
when viewed in plan,
wherein a plurality of transfer gates (102A, 102B), each of which transfers a signal
of each of the plurality of photoelectric conversion elements to an input node of
a corresponding one of the plurality of amplification means, are included,
wherein, in the second operation, one of the plurality of transfer gates corresponding
to a photoelectric conversion element from which a signal is transferred in the second
operation is conductive for at least a part of a period in which one of the plurality
of transfer gates corresponding to a photoelectric conversion element from which a
signal is transferred in the first operation is conductive, and
wherein potential of the input node of the amplification means is reset before the
first operation, and a difference process is performed on the signals obtained by
the first operation and the second operation using a reset signal output to the common
output line by the amplification means after the resetting.